The present invention relates to a method and apparatus for intermittently delivering an insoluble powder to a processing station. More particularly, the present invention relates to a method and apparatus for controlling the delivery of metal powder to an outlet arranged within a rotatable drum adapted for impact plating of the metal powder onto base metal articles.
A wet impact plating process in which metal powder particles are applied to a base metal by impacting against the surfaces of the base metal is known. In general, the parts or articles to be plated are placed within an agitator container generally in the form of a rotatable drum or barrel. Oftentimes, an impacting media, such as a mass of fine glass shot, and a suitable surface preparation agent are added to the drum with a predetermined quantity of liquid such as water for cleaning the base metal parts. The container is agitated, e.g., by rotation of the drum, in order to prepare the parts by the combined action of the impacting media and the agent. In the known methods, the parts to be plated are generally copper flashed after the surface preparation and before the actual plating process begins.
The actual plating in the prior art is accomplished by manually inserting a quantity of the plating metal in powder form within the agitator drum. Typically, a chemical plating accelerator or promoter is added along with the metal powder in an attempt to aid in proper mixing of the metal powder particles with the water contained within the agitator drum. After plating is complete, the drum is again agitated for a predetermined length of time until the parts are properly plated. Thereafter, the drum or container is opened and drained of liquids and the plated metal parts or articles are separated from the particulate impact media.
A plating process of this general type is disclosed, for example, in U.S. Pat. Nos. 3,690,935 issued Sept. 12, 1972 to Coch and 4,062,990 issued Dec. 13, 1977 to Coch.
One problem associated with these known wet impact plating methods is the control of the quantity of metal powder particles manually admitted to the drum. Such a manual insertion of the powder causes various problems in the plating process. For example, the manual insertion of the powder particles requires a stoppage of the processing and an opening of the drum to permit the introduction of the powder. Further, the quantity of powder delivered to the agitator drum may not be uniform for each charge of metal parts to be plated.
Still further, the dispersing of the insoluble metal particles within the liquid body in the drum is difficult. In other words, the agitator drum must be operated for a short period of time to properly disperse and mix the powder within the liquid in the drum. This is particularly true when the entire metal powder charge is delivered as a single batch directly into the drum. Also, such a concentration of the metal powder within a small area in the drum may lead to uneven plating of all the parts within the drum. For example, parts located close to the introduction point of the metal powder charge receive a large quantity of the plating powder initially. In contrast, parts arranged within the drum at a location spaced from the introduction point of the metal powder particles do not receive initial plating particles until after a period of agitation of the drum to disperse the particles throughout the liquid therein. The addition of a chemical accelerator or promoter along with the metal powder particles aids in mixing or dispersing the particles more quickly within the liquid in the container. However, it has been found that even with the use of such a material, the metal plating may be inconsistent from one metal part to another depending upon their location in the drum relative the point of introduction of the powder.
One proposed solution to the problem of poor plating of the metal powder onto metal parts is disclosed in U.S. Pat. No. 3,268,356 issued Aug. 23, 1966 Simon. In this patent, metal powder and/or plating promoter chemicals are incrementally provided to a plating barrel by hand or are provided at one time in the form of a slowly dissolving bar. Each of these techniques is accompanied with disadvantages. In particular, incremental addition entails the use of additional labor and may result in inaccurate measurement and/or improper timing of the increments. Additionally, where a closed horizontal drum is employed, the drum would have to be stopped so that access to its interior can be obtained. With regard to the use of a slowly dissolving bar, many factors, such as water temperature, amount and shape of the parts, rotational speed, etc., will affect the rate of dissolution. Since the bar is manufactured in a single form, the addition of metal cannot be tailored to a particular application. Other similar prior art techniques are similarly deficient for at least these reasons.
Accordingly, it is highly desirable object to develop a method and apparatus for delivering an insoluble powder automatically to an agitator drum or plating barrel. Such an automatic system should be capable of delivering a measured quantity of the powder in a generally uniform fashion to the agitator drum.
The present invention accomplishes the above desired objects and overcomes the drawbacks of the prior art. It has been discovered in the present invention that the addition of the metal powdered particles may be more carefully controlled if the particles are first prepared into a slurry for delivery to the agitator drum or other processing station. However, due to the nature of the powder particles, the delivery of the slurry entails special problems. For example, the slurry may easily clog piping or tubing used to transport the slurry to the drum after stoppage of the delivery of the slurry. Also, any discharge nozzles or outlet openings may become clogged. Still further, if an outlet is arranged within the agitator drum or plating barrel, the agitation operation within the drum forces various fluid and suspended particles back into the outlet in the container thereby further clogging the slurry delivery network.
In accordance with the present invention, these problems of slurry delivery, in addition to the problems previously mentioned with regard to the addition of metal powder particles to a processing station, are overcome. The method of intermittently delivering an insoluble powder to a processing station according to the present invention includes the steps of supplying a slurry comprised of the insoluble powder. A fluid network for supplying fluids to the processing station is pre-flushed prior to delivery of a predetermined quantity of the slurry through the fluid network to the processing station. After delivery of the slurry, the fluid network is post-flushed to remove any residual slurry.
With these steps, the present invention alleviates the aforementioned problems of both fluid within the processing station re-entering the fluid network and clogging of the fluid network by any residual slurry remaining in the fluid network after stoppage of the delivery of the slurry to the processing station. In particular, the pre-flushing of the fluid network clears any fluid and particulate matter entering the fluid delivery network from the operation of the processing station in a previous batch process which matter has clogged the outlets of the fluid network. The post-flushing of the fluid network removes any residual slurry remaining after stopping the delivery of the slurry. Further, the post-flushing ensures that the entire predetermined quantity of the slurry is delivered to the processing station. In this way, precise control over the quantity of metal powder delivered to the processing station is obtained.
In accordance with a further aspect of the present invention, the slurry is continuously agitated prior to the delivery of the slurry to the fluid network. In this way, a uniformity of the slurry, i.e., the mass quantity of metal powder particles per volume of slurry, is more effectively maintained. Still further, the present invention controls the length of time over which both the pre-flushing and the post-flushing steps occur in order to minimize the quantity of water delivered to the processing station. Such an arrangement further ensures the consistency of the processing step utilizing the metal powder slurry. In a particularly preferred embodiment, the time for pre-flushing is substantially less than the time for the post-flushing since the amount of material to be pre-flushed is substantially less than the amount of residual slurry. In accordance with a further aspect of the present invention the discharge of the slurry to the processing station is arranged to be generally uniform throughout the processing station.
An apparatus for controlling the delivery of metal powder to a rotatable drum for impact plating of base metals according to the present invention includes a supply of both water and a slurry of the metal powder. At least one outlet opening is arranged within the rotatable drum and a fluid network interconnects each of the supplies with the at least one outlet opening. A control is arranged within the fluid network for selectively individually admitting water or slurry through the fluid network to the drum in a predetermined supply sequence including a pre-flush with water, a supply of slurry and a post-flush with water.
In a preferred embodiment, the control comprises a first valve arranged between the outlet opening and the slurry supply and a second valve arranged between the outlet opening and the water supply. A control valve is provided for delivering a signal to regulate the open and closed positions of the first and second valves to accomplish the predetermined supply sequence. In accordance with the preferred embodiment, a timer is provided for actuating the control valve to deliver the signal to the appropriate one of the first and second valves for a predetermined length of time. In this way, the length of time of the pre-flush, the slurry delivery and the post-flush operations can be carefully controlled in order to minimize the amount of water added and to deliver the precise quantity of slurry, and more ularly metal powder, to the rotatable drum.
Again it is noted that by minimizing the amount of water, the processing within the drum can be more closely controlled. In particular, the relative quantities of liquid and other particles within the drum are not adversely affected by the small addition of water required for the delivery of the slurry according to the present invention.
Further in the preferred embodiment, a pump is provided in the fluid network upstream of the outlet opening for delivering the selected fluid to the outlet opening. In the preferred embodiment, a plurality of outlet openings are arranged along an elongated tube having one end connected to the fluid network and extending into the drum generally parallel to a longitudinal axis of the drum. In this way, a substantially more uniform distribution of the slurry to the drum is accomplished. In a particularly preferred embodiment, the size of the openings within the tube increases in a direction from the end connected to the fluid network to further ensure uniform distribution of the slurry to the drum.